Bone screw

ABSTRACT

The invention relates to a bone screw and a method for locking a bone screw into a bore. The bore can be provided in e.g. an implant, a plate, a nail or the like. The bone screw comprises a head portion with a first axis, a proximal shaft portion with a second axis, and a distal shaft portion with a third axis. The first axis is a center axis extending in a longitudinal direction of the head portion, the second axis is a center axis extending in a longitudinal direction of the proximal shaft portion, and the third axis is a center axis extending in a longitudinal direction of the distal shaft portion. The first and third axes are aligned to each other. The second axis is displaced relative to the first and third axes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/352,908, filed Nov. 16, 2016, which is a continuation ofInternational Application No. PCT/US2016/036669, filed Jun. 9, 2016, thedisclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The invention relates to a bone screw and a method for locking a bonescrew into a bore. The bore can be provided in e.g. an implant, a plate,a nail or the like.

Angular stable locking of implants, plates, nails or the like isassociated with positive impact on fracture healing. US 2004/0158252 A1discloses an implant for osteosynthesis, such as, for example, a bonenail, with an implant body which has at least one bore with a threadedportion and a bone screw which engages the thread when it is threadedinto a bone for the fixation of the implant body. The threaded bore hasan annular groove the diameter of which is larger than the thread outerdiameter, and which receives a ring of a deformable material with aninner diameter, which is larger than the outer diameter of the thread ofthe bone screw so that the ring extends partially into the bore.

Various designs to increase the fragment stability are commerciallyavailable. These solutions are based on modification of the lockingholes (e.g. an internal thread) and/or complex technical solutionsincluding altered operative techniques with additional implantcomponents.

However, the mentioned concepts suffer from their respective technicalcomplexity, the required costly implant, plate or nail modification bye.g. additional threads, and a missing backward compatibility toexisting implants, plates, nails or the like.

BRIEF SUMMARY OF THE INVENTION

Hence, there may be a need to provide an improved bone screw, whichallows in particular a less complex locking of a bone screw into a bore.

The problem of the present invention is solved by the subject-matters ofthe independent claims, wherein further embodiments are incorporated inthe dependent claims. It should be noted that the aspects of theinvention described in the following apply also to the bone screw andthe method for locking a bone screw into a bore.

According to the present invention, a bone screw is presented. The bonescrew can be used for angularly locking into a bore. The bore can beprovided in e.g. an implant, a plate, a nail, an intramedullary nail, arod, a pin and the like. The bore may be a circular hole, a longitudinalgroove or may have any other shape. As a result, the bone screw can beused for interlocking the screw and a bore of arbitrary shape in e.g. animplant, a plate, a nail or the like.

The bone screw comprises a head portion with a first axis, a proximalshaft portion with a second axis, and a distal shaft portion with athird axis. The proximal shaft portion may be arranged below the headportion and the distal shaft portion may be arranged below the proximalshaft portion. Outer surfaces of the proximal shaft portion and thedistal shaft portion may engage with an inner surface of the bore.

The first axis is a center axis extending in a longitudinal direction ofthe head portion, the second axis is a center axis extending in alongitudinal direction of the proximal shaft portion, and the third axisis a center axis extending in a longitudinal direction of the distalshaft portion. The first and third axes are aligned to each other. Thesecond axis is displaced relative to the first and third axes.

In other words, the bone screw may comprise a proximal shaft portion,which is eccentrically arranged relative to a head portion and a distalshaft portion of the bone screw.

The term “aligned” means that the axes are not only parallel but arecollinear or lie on each other, in other words, they are the same. Theterm “displaced” means that the axes are parallel but do not lie on eachother, in other words, they are different. The first and third axes maybe aligned with a longitudinal axis of the bore in the implant, plate,nail or the like.

The displacement between the second axis and the first and third axesmay be in the range of a few millimeters. The second axis of theproximal shaft portion may have a displacement from the third axis ofthe distal shaft portion of about 20% of the diameter of the distalshaft portion.

The second displaced axis is configured to force the distal shaftportion of the screw sideward upon screwing in of the screw into thebore. This sideward or lateral movement of the distal shaft portionleads to a tilt of the first and third axes of the screw and thereby toa tilt of the screw relative to a bore axis while a tip of the screw maystill be anchored in e.g. the bone below the implant. In other words,the screw is slightly angled inserted into the bore and thereby providesa controlled angular deviation or offset between the first and thirdscrew axes and the bore axis. By this tilt, angle, deviation or offset,the screw may be locked into or be interlocked with the bore in e.g. theimplant. The second axis may be parallel to the bore axis.

The bone screw according to the invention may provide reduced technicalcomplexity and reduced costs compared to prior art systems. The reasonmay be that no modifications of the bore are necessary. Also a backwardcompatibility to existing implants, plates, nails or the like isprovided.

Due to the slightly angled drilling and insertion of the bone screw, thebone screw according to the invention may further provide asignificantly decreased clearance and an increased axial stiffness andstability compared to prior art systems. As a result, an in particularangular stable locking of implants, plates, nails or the like isprovided, which is associated with a positive impact on fracturehealing. This is true especially for inherently unstable fracturesituations in combination but not limited to short shaft fragments, wideintramedullary canals, poor bone qualities, and/or “distal” (oppositeend to the targeting device adaptation) locking configurations like inthe treatment of distal tibia fractures.

In an example, the length of the distal shaft portion is at least threetimes the length of the proximal shaft portion. In an example, thelength of the distal shaft portion is at least four times the length ofthe proximal shaft portion. In an example, the length of the distalshaft portion is at least five times the length of the proximal shaftportion.

In an example, the outer diameter of the proximal shaft portion islarger than the outer diameter of the distal shaft portion. The outerdiameter of the proximal shaft portion may be 20% larger than the outerdiameter of the distal shaft portion. The outer diameter of the proximalshaft portion may also be essentially the same as the outer diameter ofthe distal shaft portion. In an example, a diameter of the proximalshaft portion is about 20% smaller than a diameter of the bore.

In an example, a screw thread is continuously formed on the distal shaftportion and the proximal shaft portion. In an example, there aredifferent screw threads formed on the distal shaft portion and theproximal shaft portion.

According to the present invention, also a method for locking a bonescrew into a bore of e.g. an implant is presented. The method of lockinga bone screw into a bore comprises the following steps:

-   -   a) providing a screw as described above,    -   b) screwing in a distal shaft portion of the screw into the bore        with a longitudinal axis of the distal shaft portion being        aligned with the axis of the bore, and    -   c) engaging of an outer surface of a proximal shaft portion of        the screw with an inner surface of the bore so that the        longitudinal axis of the distal shaft portion is tilted relative        to the axis of the bore upon further screwing in of the screw.

It shall be understood that the bone screw and the method for locking abone screw into a bore according to the independent claims have similarand/or identical preferred embodiments, in particular, as defined in thedependent claims. It shall be understood further that a preferredembodiment of the invention can also be any combination of the dependentclaims with the respective independent claim.

These and other aspects of the present invention will become apparentfrom and be elucidated with reference to the embodiments describedhereinafter.

The aspects may be achieved by a bone screw comprising a head portionwith a first axis (A), a proximal shaft portion with a second axis (B),and a distal shaft portion with a third axis (C). The first axis (A) isa center axis extending in a longitudinal direction of the head portion,wherein the second axis (B) is a center axis extending in a longitudinaldirection of the proximal shaft portion, and wherein the third axis (C)is a center axis extending in a longitudinal direction of the distalshaft portion. The first and third axes are aligned to each other, andthe second axis (B) is displaced relative to the first and third axes.

The second axis is spaced from the third axes in a direction transverseto the third axis and may be parallel to the first axis and third axis.The proximal and distal shaft portions of the bone screw may be threadedand the threads are preferably circular and have centers on the secondand third axis respectively. The threads of the distal shaft portion mayhave the same diameter as the threads of the proximal shaft portion orthe diameter of the threads of the proximal shaft portion may be largerthan the distal shaft portion.

The displacement between the second axis (B) and the first and thirdaxes (A, C) preferably amounts to about 20% of a diameter of the distalshaft portion. The outer diameter of the proximal shaft portion islarger than the outer diameter of the distal shaft portion. The outerdiameter of the proximal shaft portion may preferably be about 20%larger than the outer diameter of the distal shaft portion. The lengthof the distal shaft portion is preferably at least three times thelength of the proximal shaft portion.

A screw thread may be continuously formed on the distal shaft portionand the proximal shaft portion. A diameter of the proximal shaft portionis preferably about 20% smaller than a diameter of the bore in a bone.

A method of locking a bone screw in a bore is also contemplated andpreferably comprises the following steps: providing a screw havingfirst, second and third axis with the shaft having the second and thirdaxis which are offset central longitudinal axes with a screw headcentered about the first axis; screwing in a distal shaft portion of thescrew into the bore with a longitudinal axis of the distal shaft portionbeing aligned with the axis of the bore; and engaging of an outersurface of a proximal shaft portion of the screw with an inner surfaceof the bore so that the longitudinal axis of the distal shaft portion istilted relative to the axis of the bore upon further screwing in of thescrew.

The method may further comprise providing a screw having proximalthreaded portion having a first diameter and forming a bore in a bonehaving a diameter about 20% larger than the proximal threaded portionfirst diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in thefollowing with reference to the accompanying drawings:

FIG. 1 shows a schematic drawing of an example of a bone screw.

FIG. 2 shows a schematic drawing of an example of a bone screw.

FIG. 3 shows a schematic drawing of another example of a bone screw.

FIG. 4 shows basic steps of an example of a method of locking a bonescrew into a bore.

DETAILED DESCRIPTION

FIGS. 1 and 2 show schematically and exemplarily an embodiment of a bonescrew 10 according to the invention. The bone screw 10 can be used forangularly locking the bone screw 10 into a bore. The bore is hereprovided in an implant. The implant bore is here a circular hole. Thebone screw 10 comprises a head portion 11 with a first axis A, aproximal shaft portion 12 with a second axis B, and a distal shaftportion 13 with a third axis C. The proximal shaft portion 12 isarranged below the head portion 11 and the distal shaft portion 13 isarranged below the proximal shaft portion 12. A screw thread iscontinuously formed on the distal shaft portion 13 and the proximalshaft portion 12. A diameter of the proximal shaft portion 12 is about20% smaller than a diameter of the bore.

The first axis A is a center axis extending in a longitudinal directionof the head portion 11, the second axis B is a center axis extending ina longitudinal direction of the proximal shaft portion 12, and the thirdaxis C is a center axis extending in a longitudinal direction of thedistal shaft portion 13.

The first and third axes are aligned to each other, which mean they arecollinear. The second axis B is displaced relative to the first andthird axes, which means they are parallel but at different positions.The displacement Δx between the second axis B and the first and thirdaxes A and C is in the range of a few millimeters. For example, for a 5mm bone screw 10, the displacement Δx between the second axis B and thefirst and third axes A and C is in the range of 1 mm. In general, thedisplacement Δx may amount to 20% of the bone screw diameter. The secondaxis B of the proximal shaft portion 12 has a displacement from thethird axis C of the distal shaft portion 13 of about 20% of the diameterof the distal shaft portion 13. As shown in FIG. 3, the first and thirdaxes may be aligned with a longitudinal axis D of the bore in theimplant, plate, nail or the like.

The length of the distal shaft portion 13 is here about three times thelength of the proximal shaft portion 12. The outer diameter of theproximal shaft portion 12 is here essentially the same as the outerdiameter of the distal shaft portion 13.

FIGS. 2, 3 and 4 shows basic steps of an example of a method of lockinga bone screw 10 into a bore. The method of locking a bone screw 10 intoa bore comprises the following steps:

In a step S1) as shown in the left part of FIG. 2 under I, providing ascrew 10 as described above.

In a step S2) screwing in a distal shaft portion 13 of the screw 10 intothe bore with a longitudinal axis of the distal shaft portion 13 beingaligned with the axis of the bore.

In a step S3) as shown in the right part of FIG. 2 under II, engaging ofan outer surface of a proximal shaft portion 12 of the screw 10 with aninner surface of the bore so that the longitudinal axis of the distalshaft portion 13 is tilted relative to the axis of the bore upon furtherscrewing in of the screw 10.

Outer surfaces of the proximal shaft portion 12 and the distal shaftportion 13 engage with an inner surface of the bore. For example, for a5 mm bone screw 10, the bore diameter is in the range of 4 mm.

The displaced second axis B forces the distal shaft portion 13 of thescrew 10 sideward upon screwing in of the screw 10 into the bore. Thissideward or lateral movement of the distal shaft portion 13 leads to atilt of the first and third axes of the screw 10 and thereby to a tiltof the screw 10 relative to a bore axis with an angle α. The angle α maybe in a range of 5 to 30°. The second axis B is parallel to the boreaxis.

As a result, the screw 10 is slightly angled inserted into the bore andthereby provides a controlled angular deviation or offset between thefirst and third screw axes and the bore axis. By this tilt, angle,deviation or offset, the screw 10 is locked into or is interlocked withthe bore in e.g. the implant.

FIG. 3 corresponds to FIG. 2, but shows a screw 10 with an outerdiameter of the proximal shaft portion 12 being larger than the outerdiameter of the distal shaft portion 13. The outer diameter of theproximal shaft portion 12 is here about 20% larger than the outerdiameter of the distal shaft portion 13.

It has to be noted that embodiments of the invention are described withreference to different subject matters. In particular, some embodimentsare described with reference to method type claims whereas otherembodiments are described with reference to the device type claims.However, a person skilled in the art will gather from the above and thefollowing description that, unless otherwise notified, in addition toany combination of features belonging to one type of subject matter alsoany combination between features relating to different subject mattersis considered to be disclosed with this application. However, allfeatures can be combined providing synergetic effects that are more thanthe simple summation of the features.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing a claimed invention, from a study ofthe drawings, the disclosure, and the dependent claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that certain measures are re-cited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage. Any reference signs in the claimsshould not be construed as limiting the scope.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method of locking a screw in a borecomprising: providing a screw comprising: a head portion extending alonga first central axis (A); a proximal shaft portion extending along asecond central axis (B); and a distal shaft portion extending along athird central axis (C), wherein the second central axis (B) is spacedfrom the first central axis (A) in a direction transverse to the firstcentral axis (A), and wherein the second central axis (B) is spaced fromthe third central axis (C) in a direction transverse to the thirdcentral axis (C), screwing the distal shaft portion of the screw intothe bore with the third central axis (C) substantially coaxial with acentral axis of the bore, and engaging an outer surface of the proximalshaft portion of the screw with an inner surface of the bore so that thethird central axis (C) of the distal shaft portion becomes angledrelative to the central axis of the bore.
 2. The method of claim 1,further comprising engaging an outer surface of the distal shaft portionwith the inner surface of the bore.
 3. The method of claim 2, furthercomprising forming the bore such that the bore has a diameter largerthan an outer diameter of the proximal shaft portion of the screw. 4.The method of claim 3, further comprising forming the bore such that thediameter of the bore is about 20% larger than the outer diameter of theproximal shaft portion of the screw.
 5. The method of claim 3, whereinthe outer diameter of the screw provided in the providing step is 4 mmand the diameter of the bore formed in the forming step is 5 mm.
 6. Themethod of claim 1, wherein engaging the outer surface of the proximalshaft portion of the screw with the inner surface of the bore furthercomprises displacing the proximal shaft portion to force the distalshaft portion of the screw sideward in conjunction with further screwingin of the screw into the bore, the sideward movement of the distal shaftportion increasing the angle between the third central axis of thedistal shaft portion and the central axis of the bore.
 7. The method ofclaim 1, wherein the engaging step causes the third central axis of thedistal shaft portion of the screw to become angled relative to thecentral axis of the bore such that an angle between the third centralaxis and the central axis of the bore is in a range of five to thirtydegrees.
 8. The method of claim 1, wherein the engaging step furthercomprises screwing in of the screw into the bore until the angulation ofthe distal shaft portion is sufficient to lock the screw in the bore. 9.The method of claim 1, wherein the first central axis (A) of the screwprovided in the providing step is coincident with the third central axis(C).
 10. The method of claim 1, wherein the proximal shaft portion ofthe screw provided in the providing step includes a first outer diameterthat is larger than a second outer diameter of the distal shaft portionof the screw.
 11. A bone screw comprising: a head portion with a firstaxis (A); a proximal shaft portion with a second axis (B); and a distalshaft portion with a third axis (C); wherein the first axis (A) is acenter axis extending in a longitudinal direction of the head portion,wherein the second axis (B) is a center axis extending in a longitudinaldirection of the proximal shaft portion, and wherein the third axis (C)is a center axis extending in a longitudinal direction of the distalshaft portion, wherein the first axis (A) is spaced from the second axis(B) in a direction transverse to the second axis, wherein the secondaxis (B) is spaced from the third axis (C) in a direction transverse tothe third axis, wherein the proximal and distal shaft portions arethreaded, wherein the proximal shaft portion includes an outer diameterthat is larger than an outer diameter of the distal shaft portion, andwherein a screw thread is continuously formed on the distal shaftportion and the proximal shaft portion and the head portion isunthreaded.
 12. The bone screw of claim 11, wherein the outer diameterof the proximal shaft portion is about 20% larger than the outerdiameter of the distal shaft portion.
 13. The bone screw of claim 11,wherein the second axis (B) is displaced relative to the third axis (C)by an amount that is about 20% of the outer diameter of the distal shaftportion.
 14. The bone screw of claim 11, wherein the proximal shaftportion is entirely collinear with the second axis (B), the proximalshaft portion directly abutting the head portion.
 15. A bone screwcomprising: a head portion with a first axis (A); a proximal shaftportion with a second axis (B); and a distal shaft portion with a thirdaxis (C); wherein the first axis (A) is a center axis extending in alongitudinal direction of the head portion, wherein the second axis (B)is a center axis extending in a longitudinal direction of the proximalshaft portion, and wherein the third axis (C) is a center axis extendingin a longitudinal direction of the distal shaft portion, wherein thefirst axis (A) is spaced from the second axis (B) in a directiontransverse to the second axis, wherein the second axis (B) is spacedfrom the third axis (C) in a direction transverse to the third axis,wherein the proximal and distal shaft portions are threaded, wherein thedistal shaft portion has a length at least three times greater than alength of the proximal shaft portion, and wherein a screw thread iscontinuously formed on the distal shaft portion and the proximal shaftportion and the head portion is unthreaded.
 16. The bone screw of claim15, wherein the second axis (B) is displaced relative to the third axis(C) by an amount that is about 20% of the outer diameter of the distalshaft portion.
 17. The bone screw of claim 15, wherein the proximalshaft portion is entirely collinear with the second axis (B), theproximal shaft portion directly abutting the head portion.
 18. The bonescrew of claim 15, wherein the first, second and third axes are parallelwith one another.